Nerve agents are considered to be a heinous type in a chemical warfare. An organic phosphorous-based compound functioning as a class of important and fatal nerve agents is an important enzyme for a nerve system, and is a strong inhibitor of acetylcholinesterase (AChE) responsible for inhibition of acetylcholine, a neurotransmitter.
Phosphorylation of an active esteratic site of an enzyme residue by an organic phosphorous-based compound reagent causes an enzyme to be ineffective. Such an irreversible inactivation produces a large amount of acetylcholine as a result of cholinergic hyperstimulus, which leads to respiratory arrest and death within several minutes. Therefore, it is urgent to develop a method for sensitively and rapidly detecting nerve agents formed of a deadly poisonous, colorless and odorless organic phosphorous-based compound.
A design of a reactive chemosensor by esterification of an organic phosphorous-based compound nerve agent is a wise strategy in that it may rapidly detect a toxic organic phosphorous-based compound and such an approach may be used to decompose the organic phosphorous-based compound with high peculiarity.
A current method for detecting an organic phosphorous-based compound nerve agent is mainly based on colorimetric analysis, fluorescence analysis, electrochemical analysis, enzymatic analysis, or the like. However, such systems have limitations, such as low selectivity, slow reaction, complicated operation, and low portability.
Generally, since the colorimetric method uses an inexpensive apparatus, it is considered to be the simplest detection technique. The colorimetric method, however, always has a sensitivity issue at a low concentration.
In this regard, fluorescence modulation enables ideal high sensitivity signal detection. In particular, a ratiometric mode measuring the ratio of two wavelength strengths may enhance selectivity and sensitivity by removing perturbations from environmental effects.
Representative examples of organic phosphorous-based compound nerve agents are described below.

Meanwhile, a near-infrared ray (NIR) dye has come to prominence in analysis of many biological studies due to its optical properties able to image molecular activity with high penetration and low self-fluorescence background.
A tricarbocyanine dye is widely used as a fluorescent marker and a sensor for imaging in a living body because it has a high extinction coefficient and a comparatively high quantum yield, and the absorption and emission maxima occur in the near-IR region of the spectrum (650-900 nm).
Photophysical and structural properties of cyanine dyes depend on π-conjugated bridge between electron donor groups. Thus, a novel approach for cyanine dyes may be developed by disturbing a polymethine π-electron system of cyanine dyes. However, it is typically difficult to modify the cyanine structure through synthesis. Generally, a tricarbocyanine derivative is modified by nucleophillic substitution for substituting chlorine atom of tricarbocyanine having various functionalities at a meso site.
However, such a strategy is limited due to chlorine atom exhibiting a comparatively inactivity at the meso site. To avoid this limitation and to make better chemical and photochemical properties of tricarbocyanine as much as possible, a substituent having activity at the meso site of a polymethine chain is very preferable for designing various cyanine dyes.
Additionally, application of intercellular or extracellular pH change by various physiological and pathological processes is a promising strategy for analysis and diagnosis of cells. Since an infection or tumor generally makes an acidic environment, a small molecular fluorescent substance probe able to be activated in an acidic pH is a useful tool for detecting a cancer cell in an organism. However, up to now, there is almost no fluorescent probe able to be activated in an acidic pH for in vivo imaging.
Thus, the inventors of the present application have studied cyanine derivatives having a substituent having activity at a meso site of a polymethine chain, have found that the cyanine derivative having a reaction functional group substituted at the meso site is very simply synthesized, is suitable for mass production, has a very fast reaction rate because while a related art reagent for detection of nerve agents is subject to two steps of reactions, the cyanine derivative of the present invention is subject to only one step of reaction, has very excellent sensitivity, is able to be activated in an acidic pH, and is able to be used as an acid pH-activated ratiometric NIR probe, and have completed the present invention.